Possible Duplicate:
Why doesn't Bitcoin return lost coins back into the block reward?
What could be the consequences of many bitcoins being lost out of circulation if people lose their wallets?
Okay, the first question has to do with stale bitcoins. Say people lose their private keys. Over time it just keeps building, and a large portion of the 21mm bitcoins are immobilized. What happens?
The same scenario can occur for a different reason, say people start putting bitcoins in their IRAs and there millions of bitcoins held immobile. Also, how do I know that in 20 years they still will be good. Maybe the network truncates the transaction log and my part falls off.